Safety interlock system

ABSTRACT

A safety interlock system for a riding lawn mower powered by an internal combustion engine which includes a switch responsive to the engagement of the transmission, a switch responsive to the engagement of the cutting blade, a switch responsive to the operation of the engine and an ignition switch. The transmission, cutting blade and engine switches are in a circuit connected to ground whereby the ignition switch must be on and the transmission and cutting blade disengaged to start the engine. Also disclosed is an additional switch responsive to the occupation of the driver&#39;&#39;s seat disposed in parallel circuit with the engine switch, whereby, to start the engine, irrespective of the occupation of the seat, the cutting blade and transmission must be disengaged. If the operator leaves the driver&#39;&#39;s seat with either the cutting blade or the transmission engaged, the engine will stop.

United States Patent 1 Peterson [54] SAFETY INTERLOCK SYSTEM Clifford D.Peterson, Marshalltown, Iowa [75] Inventor:

[73] Assignee: Cooper Manufacturing Company,

Inc., Marshalltown, Iowa [22] Filed: Feb. 28, 1972 [21] Appl. No.:229,646

Primary ExaminerHugh R. Chamblee Assistant Examiner-J. A. OliffAttorney-A. W. Molinare, George B. Newitt, D. D. Allegretti et al.

[ 51 June 5,1973

[57] ABSTRACT A safety interlock system for a riding lawn mower poweredby an internal combustion engine which includes a switch responsive tothe engagement of the transmission, a switch responsive to theengagement of the cutting blade, a switch responsive to the operation ofthe engine and an ignition switch. The transmission, cutting blade andengine switches are in a circuit connected to ground whereby theignition switch must be on and the transmission and cutting bladedisengaged to start the engine. Also disclosed is an additional switchresponsive to the occupation of the drivers seat disposed in parallelcircuit with the engine switch, whereby, to start the engine,irrespective of the occupation of the seat, the cutting blade andtransmission must be disengaged. If the operator leaves the drivers seatwith either the cutting blade or the transmission engaged, the enginewill stop.

4 Claims, 10 Drawing Figures BACKGROUND OF THE INVENTION This inventionrelates to a riding lawn mower powered by an internal combustion engineand more particularly, to a safety interlock system for a riding lawnmower designed to insure safe operation of the mower.

Riding type or tractor-powered mowers are recognized as being inherentlydangerous mechanisms if used improperly and negligently. Each yeartractor operators and bystanders have lost or injured fingers, toes andlimbs due to their working around the tractor while the cutting blade isengaged. For example, an operator frequently dismounts the mower toremove material fouling the cutting blade. If the cutting blade isengaged and rotating when the operator is cleaning near the cuttingblade, the risk of grave physical injury is serious.

Furthermore, many tractor operators are injured during the operation orstarting of the engine. If an engine is started with either thetransmission or cutting blade engaged, the operator places an undue loadon the starting motor but, more importantly, the operator may be thrownfrom the mower by the sudden starting action of the engine. If thisunfortunate situation happens during the starting operation, theoperator may be harmed, not only by the weight of the tractor possiblypassing over him, but by the cutting action of the blade. Accordingly,it is important that both the cutting blade and transmission bedisengaged when the engine is being started. It is also important thatshould the operator of the mower be thrown from his seat during theoperation of the mower that the engine be shut off immediately toprevent injury to the operator and the mower itself.

Manufacturers of riding lawn mowers have long recognized the need forsafety systems to prevent injuries to operators. In US. Pat. No.3,521,612 (Santi et al.), there is described a safety interlock systemwherein an electronic relay switch system, containing arectifiercapacitor, is in circuit with ground and a switch cooperationwith the shift control of the transmission. In this system, thetransmission must be in neutral to start the engine. Once the engine isstarted, the relay switch is opened by current pulses emenating from themagneto primary thereby allowing the transmission to be engaged, withoutstopping the engine. I

This system does not disclose or suggest the utilization of a safetyinterlock in conjunction with a cutting blade engaging mechanism nordoes it disclose and suggest the utilization of a safety interlock inconjunction with the mower seat. Hence, the mower of Santi, could bestarted with the cutting blade engaged and would remain running if theoperator were dislodged from the seat.

Further, the rectifier-capacitor used by Santi et al to open theinterlock circuit, when the engine is once started, is an expensive,intricate mechanism not readily replaced or repaired by the typicalmower owner or operator.

In U. S. Pat. No. 3,229,452 (Hasenbank), there is disclosed an interlocksystem for a riding mower which includes a seat switch, a transmissionswitch and a cutting blade switch in circuit with the engine and ground.In the Hasenbank system, both the transmission and cutting blade must bedisengaged to start the engine when the operator is dismounted. However,when the operator is in the seat, the engine can be started if eitherthe transmission or cutting blade is engaged. Thus, in the I-Iasenbanksystem, the operator could be thrown from the mower if the engine isstarted when the transmission is engaged. While the I-Iasenbank systemoffers protection for the operator, during starting, when the operatoris dismounted; and, when the mower is continually operated, it fails toprotect the operator when he starts the engine while sitting in themower seat.

SUMMARY OF THE INVENTION An object of this invention is to provide animproved safe, efficient yet inexpensive interlock system for ariding-type lawn mower.

Another object of this invention is to provide an improved safety systemfor a riding lawn mower wherein both the transmission and cutting blademust be disengaged before the mower engine can be started, irrespectiveof the occupation of the riding seat.

It is a further object of this invention to provide an improved safetysystem for a riding lawn mower wherein the engine is automaticallystopped whenever the operator leaves the tractor seat with either thetransmission or cutting blade disengaged.

In an embodiment, this invention provides an improved safety interlocksystem for a riding lawn mower powered by an internal combustion engineand having at least one powered wheel and a cutting blade. The poweredwheel and cutting blade are engaged to the engine by separatetransmission and cutting engaging mechanisms respectively wherein bothof the mechanisms transmit power from the engine and have engaged anddisengaged positions.

The magneto on the engine is in circuit with an on-off ignition switchwhich is adapted to ground the magneto when in an off position. When theignition switch is in an on position, the magneto is disconnected fromground, thereby permitting the engine to start or continue running. Inother words, the ignition switch must be in the on position to eitherstart the engine or keep it running.

An engine switch, responsive to the operation of the engine and incircuit with the magneto of the engine is included in the system. Thisswitch is in an open position when the engine is operated and is in aclosed position when the engine is stopped. Further this engine switchcan be an electronically-activated switch such as the rectifiercapacitor electronic switch of U. S. Pat. No. 3,521 ,612 (Santi, etal.), but it is preferred that the engine switch be a switch locatedcontiguous with the blower housing enclosing the engine fly wheel andadapted to open in response to the flow of air passing through theblower housing as the fly wheel rotates. While this switch could operateon a pressure differential between the air flow within the fly wheelhousing and the atmosphere, it is preferred that the engine switch be anair vane switch wherein the vane is located within the engine housingand operates in response to air impinging on it from the fly wheel.

In a more limited embodiment, the air vane switch is opened when theflow of air in the housing exceeds a first predetermined value such aswhen the engine reaches its normal operating speed but closes when theair flow falls below a second predetermined value which is less than thefirst predetermined value. Typically, this second value corresponds toan engine speed below the stall speed of the particular engine utilized.

In circuit with the engine switch and ground is a transmission switchresponsive to the engagement of the transmission mechanism. Thistransmission switch is in an open position when the transmission isdisengaged from the engine (i.e. neutral) and is in a closed positionwhen the transmission is in an engaged position (i.e forward orreverse). Similarly in circuit with the engine switch and ground is acutting blade switch responsive to the engagement of the cuttingengagement mechanism. This cutting blade switch is in an open positionwhen the cutting blade is disengaged and is in a closed position whenthe cutting blade is engaged.

When either the transmission or cutting blade switch is in a closedposition (i.e. either mechanism is engaged) and the engine is notoperating, the engine switch will also be in a closed position therebygrounding out the magneto, thus preventing the starting of the engine.However, once the engine is properly started, the engine switch opensand the transmission and/or cutting blade can be engaged.

In one present embodiment, the interlock system includes a seat switchresponsive to the occupation of the riding seat in parallel circuit withthe engine switch. This seat switch is adapted to be in an open positionwhen the seat is occupied by the mower operator and to be in a closedposition when the seat is vacant. In this embodiment, the mower can bestarted, irrespective of the position of the seat switch (i.e. whetherthe mower seat is occupied or not) only when both the cutting andtransmission mechanisms are disengaged. However, when the engine oncestarts and is running, if the operator should leave the tractor seat(i.e. close the seat switch) with either the transmission or cuttingblade mechanisms engaged, the engine magneto will be grounded therebystopping the operation of the engine and mower. Accordingly, there 'isprovided a system which'protects the operator while he is both startingand running a riding lawn mower.

Other objects and advantages of the present invention will becomeapparent in the following description.

BRIEF DESCRIPTION OF DRAWINGS There is shown in the attached drawingpresently preferred embodiments of the present invention wherein:

FIG. 1 is a perspective view of a typical riding mower illustrating theposition of various switches which comprise the inventive safetyinterlock system;

FIG. 2 is a detailed perspective view of the riding seat and the seatswitch;

FIG. 3 is a detailed perspective view of the fly wheel housing and theengine switch;

FIG. 4 is a detailed perspective view of the transmission and thetransmission switch;

FIG. 5 is a schematic circuit diagram for a riding mower utilizing theinventive safety interlock system;

FIG. 6 is a detailed elevational view'of the engine switch mounted inthe fly wheel housing taken along section line 6-6 of FIG. 3; I

FIG. 7 is a circuit diagram of the safety interlock system wherein aseat switch is in parallel circuit with the engine switch;

FIG. 8 is a circuit diagram of a modified safety interlock systemwherein a seat switch is not utilized;

FIG. 9 is a detailed sectional elevation view of the transmission switchtaken along section line 9-9 of FIG. 4; and

FIG. 10 is a detailed plan view of the cutting blade switch taken alongsection line 10-10 of FIG. 1.

DETAILED DESCRIPTION OF THE PRESENT INVENTION Illustrated in FIG. 1 is aconventional riding mower l utilizing the inventive safety interlocksystem and equipped with rear wheel 2, at least one of which is powered,steering wheel 3, and internal combustion engine 18. A lockable ignitionswitch I7, which is in a grounded position when locked, is provided tostart engine '18. Speed selector 6 and foot brake 7 provide additionaloperational control of the mower. A cutting assembly 4 comprising aconventional rotary cutting blade or blades (not shown) and variablecutting height adjustment 5 is supported below the tractor. Cuttingblade clutch lever 8 engages and disengages the cutting assembly fromthe engine.

Transmission 26, equipped with transmission engaging lever 25 transmitspower from engine 18 to powered wheel 2. Seat 13 provides a place forthe operator or driver of the mower to sit during its operation.

The safety interlock system on the mower comprises a circuit includingground, magneto 18a, engine switch 20 actuated by the operation ofengine 18, cutting blade switch 11 actuated by blade clutch lever 8,transmission switch 27 actuated by transmission lever 25, lockableignition switch 17 and weight depressible seat switch 14. This interlocksystem, the circuitry of which is best presented in FIGS. 5, 7 and 8,provides an improved interlock system having the following features:

1. The system may be used in conjunction with an electric start ofmanual recoil start engine;

2. The component parts of the system are inexpensive and readilyreplaced;

3. The mower engine can be started by the operator while sitting in theseat or standing alongside the mower provided thatboth the transmissionand cutting blades are disengaged. In other words, the cutting blade andtransmission must always be disengaged to start the engine irrespectiveof the occupation, by the driver, of the riding seat;

4. The system includes means for preventing unauthorized use of themower;

5. The transmission and cutting blades can be engaged only if the driveris occupying the riding seat; and

6. The engine is automatically grounded and stopped if the driver shouldleave his seat with either the transmission or cutting blade engaged.

FIG. 5 illustrates a schematic circuit diagram for the interlock systemwhen used on an electric starting riding lawn mower and the relationshipbetween starting battery 33, altenator 34, magneto 18a, cutting bladeswitch 11, seat switch 14, ignition switch 17, engine switch 20,transmission switch 27 and ground. I-IOw-' ever, since the inventiveinterlock system is equally applicable to electrical starting systems aswell as manual starting systems, reference from hereon will be made tothe simplified circuit diagrams of FIGS. 7 and 8 wherein only thoseportions of the circuit necessary for a clear understanding of thepresent invention are presented.

Referring first to FIG. 8, there is illustrated a circuit comprisingmagneto 18a, cutting blade switch 111, igniopened, thereby breaking theground with the magneto. When the engine is not operating and is to bestarted, engine switch is in a closed position. When the engine switchis in this closed position, if either transmission switch 27 or cuttingblade switch 11 is closed (i.e., either the transmission or cuttingblade is engaged), the magneto 18a will be grounded out. In other words,to start the engine, the ignition switch must be on and both thetransmission and cutting blade disengaged. However, once the enginereaches its nor mal idling speed, the engine switch opens therebypermitting the engagement of the transmission and/or the cutting blade.Without the opening of engine switch 20, the magneto would be groundedupon engagement of either the transmission or the cutting blade therebystopping the engine.

Referring next to FIG. 7, there is illustrated the basic circuit of FIG.8 wherein a seat switch 14 is in parallel circuit with the engine switch20. In this preferred embodiment, as in the embodiment presented in FIG.8, the engine can be started by the operator from either a mounted ordismounted position in relationship to the seat (i.e., either electricalor manual starting). Similarly, ignition switch 17 must be opened andboth the transmission and cutting blade disengaged before the engine canstart. In other words, when the engine is not operating and is to bestarted, should either the transmission or cutting blade be engaged(switch 11 or 27 closed), the magneto will be grounded through engineswitch 20 thereby preventing the starting of the engine. It should benoted that since engine switch 20 and seat switch 14 are in parallel,they provide alternative paths for grounding the magneto. Thus, theengine cannot be started with either the transmission or cutting bladeengaged irrespective of the occupation of the driving seat since, shouldseat switch 14 be opened (i.e., seat occupied), the magneto will stillbe grounded by the engine switch.

Once the engine is running, engine switch 20 is opened thereby placingseat switch 14 as the sole controlling switch between the cutting switch11 and transmission switch 27 and ground. Therefore, if the engine isrunning and the mower seat is unoccupied (seat switch 14 closed),neither the transmission nor the cutting blade can be engaged (i.e.,switch 11 or 27 closed) without grounding the magneto and stopping theengine. However, when the mower seat is occupied, seat switch 14 will beopened (as will engine switch 20), thereby allowing the engagement ofthe transmission or cutting blade. Should the operator leave the seatwith the engine running and either the transmission or cutting bladeengaged, seat switch 14 will close thereby grounding the magneto andstopping the engine. This protects the operator of the mower should hebe thrown from the mower during its operation.

It should be noted that the safety interlock system of this invention isapplicable to any mower system utilizing an internal combustion engineirrespective of the type of transmission or cutting blade mechanismsutilized, since the exact mechanisms are not material to the operationof the invention. Accordingly, these mechanisms can comprise hydraulicsystems, meshed gear systems, friction belt systems or combinationsthereof. A typical blade and transmission mechanism is illustrated asUS. Pat. No. 3,229,452, the teachings of which are incorporated byreference herein.

The exact location and operation of the switches con tained in theinventive interlock system is best represented by reference to FIGS. 2,3, 4, 6, 9 and 10. As seen in FIG. 10, the cutting blade switch 11 isactuated responsive to movement of the blade clutch lever 8. Bladeclutch lever 8 extends vertically upward through opening 9 in the mowerchassis and moves forward and backward along this opening. Tab portion10, provided in opening 9, cooperates with clutch lever 8 to provide anotched forward, engaged position and a notched back, disengagedposition. When the clutch lever 8 is in the back, disengaged position,the clutch lever pushes member 12 of switch 11 inwards so that theswitch is in an open position. However, when the clutch lever is movedforward, it disengages depressible member 12 on switch 11, therebyallowing member 12 to move outwards, closing switch 11.

The construction. and orientation of transmission switch 27 andtransmission lever 25 is best illustrated by reference to FIG. 4 and 9.Lever 25 extends upward from transmission 26 and horizontally throughopening 29 in mounting plate 28. Depressible switch member 31 ontransmission switch 27 extends downward through opening 30 in plate 28to make contact with and coact with lever 25. Space apart, raised knobs32 on plate 28 provide lever 25 with recessed stable positions. Lever 25is biased against plate 28 so that knobs 32 provide a stable positionfor the transmission lever 25 when it is engaged or disengaged.

Transmission lever 25 moves laterally back and forth through opening 29from a neutral disengaged position (N) to an engaged forward or reversed(F or R) position, wherein the transmission, engine and wheels areengaged. AS indicated, the transmission is disengaged when lever 25 ispositioned between raised knobs 32. When in this disengaged position,lever 25 depresses switch member 31 of switch 27 inward to an openposition. When the transmission is engaged (F or R), there is no contactbetween lever 25 and switch 27 and the switch is in a closed position.

As indicated, mower 1 is provided with a seat 13 for support of anoperator of the mower when in a sitting position which coats with seatswitch 14. Referring to FIG. 2, depressible member 15 of switch 14extends vertically upward through an opening in the bottom of the seat.Mounted under the upholstery of seat 13 is a biased hinged flap 16biased to be in a generally open position which is hingedly connectedalong its rear edge to seat 13. When seat 13 is unoccupied, depressiblemember 15 extends freely upward through the seat and switch 14 is in anormal, closed position. When the seat is occupied, plate 16 pressesmember 15 downward and switch 14 is then placed in an open position.

A feature of the novel interlock system is the engine switch 20 which,as illustrated in FIGS. 3 and 6, is a vane switch mounted on fly wheelhousing 19 enclosing fly wheel 22 of engine 18. Referring to FIG. 6engine switch 20 comprises leads 23 for ready, simple connection to theinterlock circuit, depressible switch member 24 and pivotally connectedswitch vane 21 extending into the interior of housing 19. Switch 20 isinexpensively manufactured and may be replaced by an individualpossessing a minimum of mechanical skills.

Engine switch 20 is adapted to be in a closed position when the engineis not operating and to be in an open position, when the engine flywheel is rotating. More particularly, when fly wheel 22 rotates withinhousing 19, air is circulated therein and impinges on vane 21 creatingdrag forces which actuate the vane. As vane 21 moves inward asillustrated in FIG. 6, it compresses depressible member 24 inwardsthereby opening the switch. This air circulation in a typical internalcombustion engine is enhanced by cooling blades 22a (FIG. 3) which areconventional features on an engine fly wheel and can be either curved orflat.

Engine switch is preferably an over center toggle switch which openswhen the engine speed reaches a first predetermined level but closeswhen the engine speedfalls below a second predetermined level which isbelow the first level. A typical switch of this nature is a No. E22microswitch manufactured by Cherry Electric Products Corp. For example,the amount of air impinging on vane 21 is approximately proportional tothe engine speed. In other words, at higher engine speeds, more air flowis generated than at lower engine speeds. The first predetermined oropening value of the switch is preferably the normal idling speed of aninternal combustion engine (i.e., LOGO-1,800 RPM) and is appreciablyhigher than the speed generated by either a manual recoil starter or anelectric starting device. This prevents the engine switch from openinginadvertently when the engine is being turned over to start it. Thesecond predetermined or closing value of the switch is preferably belowthe stall value of an engine (i.e., less than 500-700 RPM). Thisprevents the switch from closing due to fluctuations in the engine speeddue to varying operation conditions. For example, should the enginetemporarily slow down due to the mower passing through an unusuallythick section of grass, the engine switch will not inadvertently close.In other words, the engine switch will close only when the engine isstopping or will stop because it is operating at a speed below its stallvalue.

The principles of this invention may be applied to other tractor mowersthan that illustrated. For example, reel lawn mowers, garden tractortype lawn mowers, and even farm machinery.

While I have shown a presently preferred embodiment of the invention, itwill be understood that the invention is not limited thereto since itmay be otherwise embodied within the scope of the following claims Iclaim as my invention:

1. A safety interlock system for a riding lawnmower having at least onepowered wheel and a powered cutting blade which comprises, incombination:

i. an internal combustion engine having a magneto, a fly wheel and, ablower housing enclosing said fly wheel wherein the fly wheel blows airduring the operation of the engine;

ii. a transmission mechanism for transmitting power from the engine tothe powered wheel having a neutral disengaged position and a powerengaged position;

iii. a cutting engaging mechanism, for transmitting power from theengine to the cutting blade, having a blade engaged position and a bladedisengaged position;

iv. an ignition switch in circuit with the magneto and ground having anoff position and an on position, said ignition switch grounding themagneto when the ignition is in an off position and disconnecting themagneto from ground when in an on position, said ignition switchrequired to be in an on position to start the engine;

v. an engine switch in circuit with the magneto responsive to theoperation of the engine having an open and closed position; said engineswitch being in an open position when the engine is being operated andin closed position when the engine is stopped, said engine switch beingpositioned contiguous with the blower housing and being operative toopen in response to the flow of air passed through the blower housingwhen the engine is operating, said switch further characterized as anair vane switch having an actuating vane positioned within the blowerhousing;

vi. a transmission switch in circuit with the engine switch and ground,responsive to the position of the transmission mechanism having an openand closed position, said transmission switch being in an open positionwhen the transmission mechanism is in a disengaged position and in aclosed position when the transmission mechanism is in an engagedposition;

vii. a cutting blade switch in circuit with the engine switch and groundresponsive to the position of the cutting engaging mechanism having anopen and closed position, said cutting blade switch being in an openposition when the cutting blade is disengaged, and in a closed positionwhen the blade is engaged; and,

viii. said transmission and cutting switches grounding the magneto whenin a closed position and the engine is not being operated,

ix. said engine starting operation only when the ignition switch is on,the transmission is disengaged and the blade disengaged and willcontinue operation, once started, with the transmission and blade in anyposition.

2. The safety interlock system of claim 1 wherein the air vane switch isin an open position when the flow of air in the housing exceeds a firstpredetermined value and is in a closed position when the flow of air isbelow a second predetermined value, said second value being less thanthe first value.

3. In a riding lawnmower equipped with a movable chassis, a riding seaton said chassis, an internal combustion engine having a magneto and aflywheel, a blower housing containing said flywheel; and, disengagabletransmission and cutting blade engaging mechanisms, the improved safetyinterlock system which comprises:

i. an ignition switch in circuit with the magneto and ground, saidignition switch having an open and closed position grounding the magnetowhen closed so that the ignition switch must be open to start theengine;

ii. an engine switch in circuit with the magneto responsive to theoperation of the engine said engine switch being in an open positionwhen the engine is being operated and in a closed position when theengine'is stopped;

iii. said engine switch comprising an air vane switch having anactuating vane positioned within the blower housing, said vane openingthe engine switch in response to air flow in the blower housing when theengine is running;

iv. a seat switch in parallel circuit with the engine switch responsiveto the occupation of the riding seat having an open position and closedposition, said seat switch being in an open position when the seat isoccupied and in a closed position when the seat is vacant;

. a transmission switch in circuit with the engine and seat switches andground responsive to the engagement of the transmission mechanism havingan open and closed position; said transmission switch being in openposition when the transmission is disengaged and in a closed positionwhen the transmission is engaged;

vi. a cutting blade switch in circuit with the engine vii. saidtransmission and cutting switches grounding the magneto when in a closedposition and the engine is not being operated irrespective of theoccupation of the riding seat and allowing the engine to start only ifboth the transmission and cutting blade engaging mechanism aredisengaged and permitting continued operation when started with eitherthe transmission or cutting blade engaged only if the riding seat isoccupied.

4. A safety interlock system as in claim 3 wherein the air vane switchis in an open position when the flow of air in the housing exceeds afirst predetermined value and is in a closed position when the flow ofair is below a second predetermined value, said second value being lessthan the first value.

1. A safety interlock system for a riding lawnmower having at least onepowered wheel and a powered cutting blade which comprises, incombination: i. an internal combustion engine having a magneto, a flywheel and, a blower housing enclosing said fly wheel wherein the flywheel blows air during the operation of the engine; ii. a transmissionmechanism for transmitting power from the engine to the powered wheelhaving a neutral disengaged position and a power engaged position; iii.a cutting engaging mechanism, for transmitting power from the engine tothe cutting blade, having a blade engaged position and a bladedisengaged position; iv. an ignition switch in circuit with the magnetoand ground having an off position and an on position, said ignitionswitch grounding the magneto when the ignition is in an off position anddisconnecting the magneto from ground when in an on position, saidignition switch required to be in an on position to start the engine; v.an engine switch in circuit with the magneto responsive to the operationof the engine having an open and closed position; said engine switchbeing in an open position when the engine is being operated and inclosed position when the engine is stopped, said engine switch beingpositioned contiguous with the blower housing and being operative toopen in response to the flow of air passed through the blower housingwhen the engine is operating, said switch further characterized as anair vane switch having an actuating vane positioned within the blowerhousing; vi. a transmission switch in circuit with the engine switch andground, responsive to the position of the transmission mechanism havingan open and closed position, said transmission switch being in an openposition when the transmission mechanism is in a disengaged position andin a closed position when the transmission mechanism is in an engagedposition; vii. a cutting blade switch in circuit with the engine switchand ground responsive to the position of the cutting engaging mechanismhaving an open and closed position, said cutting blade switch being inan open position when the cutting blade is disengaged, and in a closedposition when the blade is engaged; and, viii. said transmission andcutting switches grounding the magneto when in a closed position and theengine is not being operated, ix. said engine starting operation onlywhen the ignition switch is on, the transmission is disengaged and theblade disengaged and will continue operation, once started, with thetransmission and blade in any position.
 2. The safety interlock systemof claim 1 wherein the air vane switch is in an open position when theflow of air in the housing exceeds a first predetermined value and is ina closed position when the flow of air is below a second predeterminedvalue, said second value being less than the first value.
 3. In a ridinglawnmower equipped with a movable chassis, a riding seat on saidchassis, an internal combustion engine having a magneto and a flywheel,a blower housing containing said flywheel; and, disengagabletransmission and cutting blade engaging mechanisms, the improved safetyinterlock system which comprises: i. an ignition switch in circuit withthe magneto and ground, said ignition switch having an open and closedposition grounding the magneto when closed so that the ignition switchmust be open to start the engine; ii. an engine switch in circuit withthe magneto responsive to the operation of the engine said engine switchbeing in an open position when the engine is being operated and in aclosed position when the engine is stopped; iii. said engine switchcomprising an air vane switch having an actuating vane positioned withiNthe blower housing, said vane opening the engine switch in response toair flow in the blower housing when the engine is running; iv. a seatswitch in parallel circuit with the engine switch responsive to theoccupation of the riding seat having an open position and closedposition, said seat switch being in an open position when the seat isoccupied and in a closed position when the seat is vacant; v. atransmission switch in circuit with the engine and seat switches andground responsive to the engagement of the transmission mechanism havingan open and closed position; said transmission switch being in openposition when the transmission is disengaged and in a closed positionwhen the transmission is engaged; vi. a cutting blade switch in circuitwith the engine and seat switches and ground responsive to theengagement of the cutting blade engaging mechanism having an open andclosed position, said cutting blade switch being in an open positionwhen the cutting mechanism is disengaged and being in a closed positionwhen engaged; and vii. said transmission and cutting switches groundingthe magneto when in a closed position and the engine is not beingoperated irrespective of the occupation of the riding seat and allowingthe engine to start only if both the transmission and cutting bladeengaging mechanism are disengaged and permitting continued operationwhen started with either the transmission or cutting blade engaged onlyif the riding seat is occupied.
 4. A safety interlock system as in claim3 wherein the air vane switch is in an open position when the flow ofair in the housing exceeds a first predetermined value and is in aclosed position when the flow of air is below a second predeterminedvalue, said second value being less than the first value.